The use of disposable cartridges of caulking material is not only now well established but has become the near universal system for the dispensing of caulking compounds, various sealants and other viscous materials. While hand actuated caulking guns are well known and well established, for a variety of reasons there is a growing demand for powered caulking guns.
Professionals, such as those employed in the construction trade, can suffer excessive fatigue from performing tasks such as applying adhesives to joists and studs when sheet flooring or wall boards are being installed. The fatigue problem is exacerbated when material is being dispensed in a cold environment because the viscosity of the material increases and higher dispensing forces are required. Indeed, the use of hand actuated caulking guns for such tasks can result in injuries such as carpal tunnel syndrome.
Automobile windshields represent another reason there is a demand for power assisted caulking guns. With many current automotive designs, the windshields have become structural parts of automobiles. In order for a windshield to function as a structural part, a windshield is securely bonded to a surrounding metal frame. The adhesive materials used for this windshield bonding, especially for replacement windshields, have high viscosity, and dispensing such an adhesive material from a cartridge requires extremely high dispensing forces. As a consequence, the installation of such windshields requires a material dispensing gun with which significant force is applied to the material to cause its dispensing.
Air actuated caulking guns which utilize compressed air are known. One commercially successful air actuated gun is described in U.S. Pat. No. 5,181,636 issued Jan. 26, 1993 under the title Incremental Dispensing Device and assigned to the assignee of this patent. Most notably the embodiment shown in FIGS. 4 through 7 of that patent has enjoyed good success in such applications as the dispensing of adhesives on joists for securement of subflooring. While this air actuated gun has enjoyed success, attempts to provide truly portable battery powered caulking guns have enjoyed only limited success.
With most caulking guns, a rod or equivalent dispensing mechanism engages a piston of a caulking tube cartridge and drives the piston toward the outlet to expel viscous material from the cartridge. Once the material in a cartridge has been expended, it is desirable for the operator to very quickly retract the dispensing mechanism to enable a spent cartridge to be removed from the gun and a new cartridge to be inserted in it. Another shortcoming of prior proposals for battery operated guns is that most, if not all, prior proposals and commercially available guns have not included a construction which provided truly simple and quick retraction of a dispensing mechanism.
Applications in which prior battery operated caulking guns could be utilized have been limited by the dispensing forces that could be generated. As an example, prior battery operated guns were not capable of generating sufficient force to dispense the sealants used to fix a replacement automotive windshield to its surrounding metal frame. Neither were they capable of dispensing construction adhesives in colder climates because even if capable of dispensing such adhesives under cold conditions, flow rates were unacceptably slow. Another disadvantage of prior battery operated dispensers has been that the power requirements were excessively high. The result has been that the number of tubes of material that could be dispensed in a battery discharge cycle was unacceptably low.
A number of proposals have utilized a threaded rod as the mechanism to transmit expelling force to a viscous material cartridge piston. With a number of these it has been proposed that the threaded rod be engaged by a split nut or claw. With these proposals a manually actuated member would be provided to shift the nut components between a rod engaged position for dispensing and a rod release position for rod retraction.
With another proposal a cam would drive an elongate washer which would frictionally engage a dispensing rod when dispensing force is applied to the washer by the cam. This proposal suggests provision of a manually operated release screw for selective release of the washer, referred to by a patentee as a "holding plate", to allow manually retraction of the rod.
In another proposal, a toothed rod is provided which has a smooth surface over a large portion of its circumference. Drive and hold detents engage the rod teeth when the rod is being advanced. For retraction the rod is rotated until a smooth surface engages the detents to allow retraction.
With other proposals it has been necessary to have a reversible motor and to drive the motor in a reverse direction for drive mechanism retraction. Still another proposal would use a plug to expand an expansible threaded element into engagement with the drive gear when the tube is advanced and to release the tube from the gear for manual retraction. A further proposal utilized a rack release button which had to be depressed simultaneously with applying retractive force to the rack to achieve manual rack retraction.
A commercially available battery operated caulking gun utilizes collapsing racks to provide a relatively short gun. Retraction of the collapsing racks for replacing a spent cartridge with a fresh cartridge requires the application of a substantial manually applied pressure after a spent cartridge has been manually removed from the gun. To enable such removal, the cartridge holding portion of the gun includes a pivotal end cover. The cover is selectively positionable in an overlapping relationship with the end of a caulking tube in a use position and pivotal to a retract position to allow extraction of a spent tube from the gun. Thus, there is no provision for collapsing the racks relatively in preparation of the gun for receiving a new cartridge unless the spent cartridge is first removed. Accordingly, there is, as compared with other modern caulking guns, undue complexity for the cartridge retention function.